Integrated circuit including vertical diode

ABSTRACT

An integrated circuit includes a vertical diode defined by crossed line lithography.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______, Attorney Docket Number 2007P50327US/I331.364.101, entitled “INTEGRATED CIRCUIT INCLUDING VERTICAL DIODE,” filed on the same date as the present application, which is incorporated herein by reference.

BACKGROUND

One type of memory is resistive memory. Resistive memory utilizes the resistance value of a memory element to store one or more bits of data. For example, a memory element programmed to have a high resistance value may represent a logic “1” data bit value and a memory element programmed to have a low resistance value may represent a logic “0” data bit value. Typically, the resistance value of the memory element is switched electrically by applying a voltage pulse or a current pulse to the memory element.

One type of resistive memory is phase change memory. Phase change memory uses a phase change material in the resistive memory element. The phase change material exhibits at least two different states. The states of the phase change material may be referred to as the amorphous state and the crystalline state, where the amorphous state involves a more disordered atomic structure and the crystalline state involves a more ordered lattice. The amorphous state usually exhibits higher resistivity than the crystalline state. Also, some phase change materials exhibit multiple crystalline states, e.g. a face-centered cubic (FCC) state and a hexagonal closest packing (HCP) state, which have different resistivities and may be used to store bits of data. In the following description, the amorphous state generally refers to the state having the higher resistivity and the crystalline state generally refers to the state having the lower resistivity.

Phase changes in the phase change materials may be induced reversibly. In this way, the memory may change from the amorphous state to the crystalline state and from the crystalline state to the amorphous state in response to temperature changes. The temperature changes of the phase change material may be achieved by driving current through the phase change material itself or by driving current through a resistive heater adjacent the phase change material. With both of these methods, controllable heating of the phase change material causes controllable phase change within the phase change material.

A phase change memory including a memory array having a plurality of memory cells that are made of phase change material may be programmed to store data utilizing the memory states of the phase change material. One way to read and write data in such a phase change memory device is to control a current and/or a voltage pulse that is applied to the phase change material. The level of current and/or voltage generally corresponds to the temperature induced within the phase change material in each memory cell.

To achieve higher density phase change memories, a phase change memory cell can store multiple bits of data. Multi-bit storage in a phase change memory cell can be achieved by programming the phase change material to have intermediate resistance values or states, where the multi-bit or multilevel phase change memory cell can be written to more than two states. If the phase change memory cell is programmed to one of three different resistance levels, 1.5 bits of data per cell can be stored. If the phase change memory cell is programmed to one of four different resistance levels, two bits of data per cell can be stored, and so on. To program a phase change memory cell to an intermediate resistance value, the amount of crystalline material coexisting with amorphous material and hence the cell resistance is controlled via a suitable write strategy.

Higher density phase change memories can also be achieved by reducing the physical size of each memory cell. Increasing the density of a phase change memory increases the amount of data that can be stored within the memory while at the same time typically reducing the cost of the memory.

For these and other reasons, there is a need for the present invention.

SUMMARY

One embodiment provides an integrated circuit. The integrated circuit includes a vertical diode defined by crossed line lithography.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles of the invention. Other embodiments of the present invention and many of the intended advantages of the present invention will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.

FIG. 1 is a block diagram illustrating one embodiment of a system.

FIG. 2 is a diagram illustrating one embodiment of a memory device.

FIG. 3 illustrates a cross-sectional view of one embodiment of a memory cell.

FIG. 4 illustrates a cross-sectional view of another embodiment of a memory cell.

FIG. 5 illustrates a cross-sectional view of another embodiment of a memory cell.

FIG. 6 illustrates a cross-sectional view of another embodiment of a memory cell.

FIG. 7 illustrates a cross-sectional view of another embodiment of a memory cell.

FIG. 8 illustrates a cross-sectional view of one embodiment of a wafer after forming an N+ region layer, an N− region layer, and a P+ region layer.

FIG. 9 illustrates a cross-sectional view of one embodiment of the wafer after forming a silicide layer.

FIG. 10A illustrates a cross-sectional view of one embodiment of the wafer after depositing an electrode material layer.

FIG. 10B illustrates a cross-sectional view of one embodiment of the wafer after depositing a first electrode material layer, an etch stop material layer, and a second electrode material layer.

FIG. 10C illustrates a cross-sectional view of one embodiment of the wafer after depositing a first electrode material layer, an etch stop material layer, and a second electrode material layer.

FIG. 10D illustrates a cross-sectional view of one embodiment of the wafer after depositing a first electrode material layer and a second electrode material layer.

FIG. 11 illustrates a cross-sectional view of one embodiment of the wafer after forming a mask.

FIG. 12 illustrates a cross-sectional view of one embodiment of the wafer after etching the electrode material layer.

FIG. 13 illustrates a cross-sectional view of one embodiment of the wafer after depositing a spacer material layer.

FIG. 14 illustrates a cross-sectional view of one embodiment of the wafer after etching the spacer material layer.

FIG. 15 illustrates a cross-sectional view of one embodiment of the wafer after etching trenches.

FIG. 16 illustrates a cross-sectional view of one embodiment of the wafer after depositing dielectric material into the trenches.

FIG. 17 illustrates a cross-sectional view of one embodiment of the wafer perpendicular to the cross-sectional view illustrated in FIG. 16.

FIG. 18 illustrates a cross-sectional view of one embodiment of the wafer after forming a mask.

FIG. 19 illustrates a cross-sectional view of one embodiment of the wafer after etching the lines of electrode material.

FIG. 20 illustrates a cross-sectional view of one embodiment of the wafer after depositing a spacer material layer.

FIG. 21 illustrates a cross-sectional view of one embodiment of the wafer after etching the spacer material layer.

FIG. 22 illustrates a cross-sectional view of one embodiment of the wafer after etching trenches.

FIG. 23 illustrates a cross-sectional view of one embodiment of the wafer after depositing dielectric material into the trenches.

FIG. 24 illustrates a cross-sectional view of one embodiment of the wafer after depositing a phase change material layer and an electrode material layer.

FIG. 25 illustrates a cross-sectional view of one embodiment of the wafer after etching the electrode material layer and the phase change material layer.

FIG. 26 illustrates a cross-sectional view of one embodiment of the wafer after depositing an encapsulation material layer and a dielectric material layer.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

FIG. 1 is block diagram illustrating one embodiment of a system 90. System 90 includes a host 92 and a memory device 100. Host 92 is communicatively coupled to memory device 100 through communication link 94. Host 92 includes a computer (e.g., desktop, laptop, handheld), portable electronic device (e.g., cellular phone, personal digital assistant (PDA), MP3 player, video player), or any other suitable device that uses memory. Memory device 100 provides memory for host 92. In one embodiment, memory device 100 includes a phase change memory device or other suitable resistive or resistivity changing memory device.

FIG. 2 is a diagram illustrating one embodiment of memory device 100. Memory device 100 includes a write circuit 124, a controller 120, a memory array 102, and a sense circuit 126. Memory array 102 includes a plurality of resistive memory cells 104 a-104 d (collectively referred to as resistive memory cells 104), a plurality of bit lines (BLs) 112 a-112 b (collectively referred to as bit lines 112), and a plurality of word lines (WLs) 110 a-110 b (collectively referred to as word lines 110). In one embodiment, resistive memory cells 104 are phase change memory cells. In other embodiments, resistive memory cells 104 are another suitable type of resistive memory cells or resistivity changing memory cells.

Each memory cell 104 includes a phase change element 106 and a diode 108. By using diodes 108 to access bits within memory array 102, a 4F² memory cell size is achieved, where “F” is the minimum lithographic feature size. Memory cells 104 are fabricated using crossed line lithography. Spacers formed on sidewalls of an electrode are used to define self-aligned vertical diodes 108 for accessing phase change elements 106.

As used herein, the term “electrically coupled” is not meant to mean that the elements must be directly coupled together and intervening elements may be provided between the “electrically coupled” elements.

Memory array 102 is electrically coupled to write circuit 124 through signal path 125, to controller 120 through signal path 121, and to sense circuit 126 through signal path 127. Controller 120 is electrically coupled to write circuit 124 through signal path 128 and to sense circuit 126 through signal path 130. Each phase change memory cell 104 is electrically coupled to a word line 110 and a bit line 112. Phase change memory cell 104 a is electrically coupled to bit line 112 a and word line 110 a, and phase change memory cell 104 b is electrically coupled to bit line 112 a and word line 110 b. Phase change memory cell 104 c is electrically coupled to bit line 112 b and word line 110 a, and phase change memory cell 104 d is electrically coupled to bit line 112 b and word line 110 b.

Each phase change memory cell 104 includes a phase change element 106 and a diode 108. Phase change memory cell 104 a includes phase change element 106 a and diode 108 a. One side of phase change element 106 a is electrically coupled to bit line 112 a, and the other side of phase change element 106 a is electrically coupled to one side of diode 108 a. The other side of diode 108 a is electrically coupled to word line 110 a. In another embodiment, the polarity of diode 108 a is reversed.

Phase change memory cell 104 b includes phase change element 106 b and diode 108 b. One side of phase change element 106 b is electrically coupled to bit line 112 a, and the other side of phase change element 106 b is electrically coupled to one side of diode 108 b. The other side of diode 108 b is electrically coupled to word line 110 b.

Phase change memory cell 104 c includes phase change element 106 c and diode 108 c. One side of phase change element 106 c is electrically coupled to bit line 112 b and the other side of phase change element 106 c is electrically coupled to one side of diode 108 c. The other side of diode 108 c is electrically coupled to word line 110 a.

Phase change memory cell 104 d includes phase change element 106 d and diode 108 d. One side of phase change element 106 d is electrically coupled to bit line 112 b and the other side of phase change element 106 d is electrically coupled to one side of diode 108 d. The other side of diode 108 d is electrically coupled to word line 110 b.

In another embodiment, each phase change element 106 is electrically coupled to a word line 110 and each diode 108 is electrically coupled to a bit line 112. For example, for phase change memory cell 104 a, one side of phase change element 106 a is electrically coupled to word line 110 a. The other side of phase change element 106 a is electrically coupled to one side of diode 108 a. The other side of diode 108 a is electrically coupled to bit line 112 a.

In one embodiment, each resistive memory element 106 is a phase change element that comprises a phase change material that may be made up of a variety of materials in accordance with the present invention. Generally, chalcogenide alloys that contain one or more elements from Group VI of the periodic table are useful as such materials. In one embodiment, the phase change material is made up of a chalcogenide compound material, such as GeSbTe, SbTe, GeTe, or AgInSbTe. In another embodiment, the phase change material is chalcogen free, such as GeSb, GaSb, InSb, or GeGaInSb. In other embodiments, the phase change material is made up of any suitable material including one or more of the elements Ge, Sb, Te, Ga, As, In, Se, and S. The phase change material can be undoped or doped with other suitable elements or combinations of elements, such as N or SiO₂.

Each phase change element may be changed from an amorphous state to a crystalline state or from a crystalline state to an amorphous state under the influence of temperature change. The amount of crystalline material coexisting with amorphous material in the phase change material of one of the phase change elements thereby defines two or more states for storing data within memory device 100. In the amorphous state, a phase change material exhibits significantly higher resistivity than in the crystalline state. Therefore, the two or more states of the phase change elements differ in their electrical resistivity. In one embodiment, the two or more states are two states and a binary system is used, wherein the two states are assigned bit values of “0” and “1”. In another embodiment, the two or more states are three states and a ternary system is used, wherein the three states are assigned bit values of “0”, “1”, and “2”. In another embodiment, the two or more states are four states that are assigned multi-bit values, such as “00”, “01”, “10”, and “11”. In other embodiments, the two or more states can be any suitable number of states in the phase change material of a phase change element.

Controller 120 includes a microprocessor, microcontroller, or other suitable logic circuitry for controlling the operation of memory device 100. Controller 120 controls read and write operations of memory device 100 including the application of control and data signals to memory array 102 through write circuit 124 and sense circuit 126. In one embodiment, write circuit 124 provides voltage pulses through signal path 125 and bit lines 112 to memory cells 104 to program the memory cells. In other embodiments, write circuit 124 provides current pulses through signal path 125 and bit lines 112 to memory cells 104 to program the memory cells.

Sense circuit 126 reads each of the two or more states of memory cells 104 through bit lines 112 and signal path 127. In one embodiment, to read the resistance of one of the memory cells 104, sense circuit 126 provides current that flows through one of the memory cells 104. Sense circuit 126 then reads the voltage across that one of the memory cells 104. In another embodiment, sense circuit 126 provides voltage across one of the memory cells 104 and reads the current that flows through that one of the memory cells 104. In another embodiment, write circuit 124 provides voltage across one of the memory cells 104 and sense circuit 126 reads the current that flows through that one of the memory cells 104. In another embodiment, write circuit 124 provides current that flows through one of the memory cells 104 and sense circuit 126 reads the voltage across that one of the memory cells 104.

In one embodiment, during a “set” operation of phase change memory cell 104 a, a set current or voltage pulse is selectively enabled by write circuit 124 and sent through bit line 112 a to phase change element 106 a thereby heating phase change element 106 a above its crystallization temperature (but usually below its melting temperature). In this way, phase change element 106 a reaches its crystalline state or a partially crystalline and partially amorphous state during this set operation.

During a “reset” operation of phase change memory cell 104 a, a reset current or voltage pulse is selectively enabled by write circuit 124 and sent through bit line 112 a to phase change element 106 a. The reset current or voltage quickly heats phase change element 106 a above its melting temperature. After the current or voltage pulse is turned off, phase change element 106 a quickly quench cools into the amorphous state or a partially amorphous and partially crystalline state.

Phase change memory cells 104 b-104 d and other phase change memory cells 104 in memory array 102 are set and reset similarly to phase change memory cell 104 a using a similar current or voltage pulse. In other embodiments, for other types of resistive memory cells, write circuit 124 provides suitable programming pulses to program the resistive memory cells 104 to the desired state.

FIG. 3 illustrates a cross-sectional view of one embodiment of a memory cell 200 a. In one embodiment, each memory cell 104 is similar to memory cell 200 a. In one embodiment, memory cell 200 a is a mushroom memory cell. Memory cell 200 a includes a P substrate 202, an N+ word line 204, an N− region 206, a P+ region 208, a silicide contact 210, a bottom electrode 212 a, a phase change element 218, a top electrode 220, spacers 224, dielectric material 222, encapsulation material 228, and dielectric material 226. P+ region 208 and N− region 206 form a diode 108. In another embodiment, the doping of regions 204, 206, and 208 are inverted, such that the polarity of diode 108 is reversed. Bottom electrode 212 a includes a first portion 214 and a second portion 216. First portion 214 has a greater cross-sectional width than second portion 216.

Word line 204 includes an N+ region formed using epitaxy, ion implantation into the P substrate, or a combination of epitaxy and ion implantation. The top of word line 204 contacts the bottom of N− region 206. N− region 206 is formed using epitaxy, ion implantation into the P substrate, or a combination of epitaxy and ion implantation. The top of N− region 206 contacts the bottom of P+ region 208. P+ region 208 is formed using epitaxy, ion implantation into the P substrate, or a combination of epitaxy and ion implantation. The top of P+ region 208 contacts the bottom of silicide contact 210. Silicide contact 210 includes CoSi, TiSi, NiSi, NiPtSi, WSi_(x), TaSi, or other suitable silicide.

The top of silicide contact 210 contacts the bottom of first portion 214 of bottom electrode 212 a. Bottom electrode 212 a includes TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, TaAlN, Cu, WN, C, or other suitable electrode material. Second portion 216 of bottom electrode 212 a is laterally surrounded by spacers 224. Spacers 224 include SiN, SiO₂, SiO_(x)N, or other suitable spacer material. Sidewalls of spacers 224 are self-aligned with sidewalls of first portion 214 of bottom electrode 212 a, the sidewalls of silicide contact 210, the sidewalls of P+ region 208, and the sidewalls of N− region 206.

The top of second portion 216 of bottom electrode 212 a contacts the bottom of phase change element 218. Phase change element 218 provides a storage location for storing one or more bits of data. The active or phase change region of phase change element 218 is at the interface between phase change element 218 and bottom electrode 212 a. The top of phase change element 218 contacts the bottom of top electrode 220. Top electrode 220 includes TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TIAlN, Cu, WN, C, or other suitable electrode material.

Dielectric material 222 laterally surrounds N− region 206, P+ region 208, silicide contact 210, bottom electrode 212 a, and spacers 224. In one embodiment, dielectric material 222 extends slightly into N+ word line 204 as indicated at 205. Dielectric material 222 includes SiO₂, SiO_(x), SiN, fluorinated silica glass (FSG), boro-phosphorous silicate glass (BPSG), boro-silicate glass (BSG), or other suitable dielectric material. Encapsulation material 228 laterally surrounds phase change element 218 and top electrode 220. Encapsulation material 228 includes SiN, SiON, or other suitable encapsulation material. In one embodiment, more than one layer of encapsulation material laterally surrounds phase change element 218 and top electrode 220. In one embodiment, encapsulation material 228 contacts a portion of the top of top electrode 220. Dielectric material 226 laterally surrounds encapsulation material 228. Dielectric material 226 includes SiO₂, SiO_(x), SiN, FSG, BPSG, BSG, or other suitable dielectric material.

The current path through memory cell 200 a is from top electrode 220 through phase change element 218 to bottom electrode 212 a. From bottom electrode 212 a, the current flows through silicide contact 210 and the diode formed by P+ region 208 and N− region 206. From N− region 206 the current flows through N+ word line 204. The cross-sectional width of the interface area between phase change element 218 and bottom electrode 212 a defines the current density through the interface and thus the power needed to program memory cell 200 a. By reducing the cross-sectional width of the interface area, the current density is increased, thus reducing the power used to program memory cell 200 a.

During operation of memory cell 200 a, current or voltage pulses are applied between top electrode 220 and word line 204 to program memory cell 200 a. During a set operation of memory cell 200 a, a set current or voltage pulse is selectively enabled by write circuit 124 and sent through a bit line to top electrode 220. From top electrode 220, the set current or voltage pulse passes through phase change element 218 thereby heating the phase change material above its crystallization temperature (but usually below its melting temperature). In this way, the phase change material reaches a crystalline state or a partially crystalline and partially amorphous state during the set operation.

During a reset operation of memory cell 200 a, a reset current or voltage pulse is selectively enabled by write circuit 124 and sent through a bit line to top electrode 220. From top electrode 220, the reset current or voltage pulse passes through phase change element 218. The reset current or voltage quickly heats the phase change material above its melting temperature. After the current or voltage pulse is turned off, the phase change material quickly quench cools into an amorphous state or a partially amorphous and partially crystalline state.

FIG. 4 illustrates a cross-sectional view of another embodiment of a memory cell 200 b. In one embodiment, each memory cell 104 is similar to memory cell 200 b. Memory cell 200 b is similar to memory cell 200 a previously described and illustrated with reference to FIG. 3, except that in memory cell 200 b, bottom electrode 212 a is replaced with bottom electrode 212 b.

In this embodiment, bottom electrode 212 b is laterally surrounded by spacers 224. The top of silicide contact 210 contacts the bottom of spacers 224 and the bottom of bottom electrode 212 b. Memory cell 200 b is programmed similarly to memory cell 200 a previously described and illustrated with reference to FIG. 3.

FIG. 5 illustrates a cross-sectional view of another embodiment of a memory cell 200 c. In one embodiment, each memory cell 104 is similar to memory cell 200 c. Memory cell 200 c is similar to memory cell 200 a previously described and illustrated with reference to FIG. 3, except that in memory cell 200 c, bottom electrode 212 a is replaced with bottom electrode 212 c.

In this embodiment, bottom electrode 212 c includes a first portion 230, a second portion 232, and a third portion 216. First portion 230 and second portion 232 have the same cross-sectional width. First portion 230 and second portion 232 have a greater cross-sectional width than third portion 216. First portion 230 and third portion 216 include the same electrode material. Second portion 232 includes an etch stop material.

The top of silicide contact 210 contacts the bottom of first portion 230. The top of first portion 230 contacts the bottom of second portion 232. The top of second portion 232 contacts the bottom of spacers 224 and the bottom of third portion 216. Etch stop second portion 232 provides an etch endpoint for the etching of the electrode material layer used to fabricate third portion 216 of bottom electrode 212 c during the fabrication process of memory cell 200 c. Memory cell 200 c is programmed similarly to memory cell 200 a previously described and illustrated with reference to FIG. 3.

FIG. 6 illustrates a cross-sectional view of another embodiment of a memory cell 200 d. In one embodiment, each memory cell 104 is similar to memory cell 200 d. Memory cell 200 d is similar to memory cell 200 a previously described and illustrated with reference to FIG. 3, except that in memory cell 200 d bottom electrode 212 a is replaced with bottom electrode 212 d.

In this embodiment, bottom electrode 212 d includes a first portion 234 and a second portion 216. First portion 234 has a greater cross-sectional width than second portion 216. First portion 234 includes a first electrode material and second portion 216 includes a second electrode material different than the first electrode material. The top of silicide contact 210 contacts the bottom of first portion 234. The top of first portion 234 contacts the bottom of spacers 224 and the bottom of second portion 216. First portion 234 provides an etch endpoint for the etching of the electrode material layer used to fabricate second portion 216 of bottom electrode 212 d during the fabrication process of memory cell 200 d. In addition, by selecting electrode materials having different resistivities for first portion 234 and second portion 216, the heat generation within bottom electrode 212 d is optimized. Memory cell 200 d is programmed similarly to memory cell 200 a previously described and illustrated with reference to FIG. 3.

FIG. 7 illustrates a cross-sectional view of another embodiment of a memory cell 200 e. In one embodiment, each memory cell 104 is similar to memory cell 200 e. Memory cell 200 e is similar to memory cell 200 a previously described and illustrated with reference to FIG. 3, except that in memory cell 200 e bottom electrode 212 a is replaced with bottom electrode 212 e.

In this embodiment, bottom electrode 212 e includes a first portion 234, a second portion 232, and a third portion 216. First portion 234 and second portion 232 have the same cross-sectional width. First portion 234 and second portion 232 have a greater cross-sectional width than third portion 216. First portion 234 and third portion 216 include different electrode materials. Second portion 232 includes an etch stop material.

The top of silicide contact 210 contacts the bottom of first portion 234. The top of first portion 234 contacts the bottom of second portion 232. The top of second portion 232 contacts the bottom of spacers 224 and the bottom of third portion 216. Etch stop second portion 232 provides an etch endpoint for the etching of the electrode material layer used to fabricate third portion 216 of bottom electrode 212 e during the fabrication process of memory cell 200 e. In addition, by selecting electrode materials having different resistivities for first portion 234 and third portion 216, the heat generation within bottom electrode 212 e is optimized. Memory cell 200 e is programmed similarly to memory cell 200 a previously described and illustrated with reference to FIG. 3.

The following FIGS. 8-26 illustrate embodiments for fabricating memory cells 200 a-200 e previously described and illustrated with reference to FIGS. 3-7.

FIG. 8 illustrates a cross-sectional view of one embodiment of a wafer 240 after forming an N+ region layer 204 a, an N− region layer 206 a, and a P+ region layer 208 a. In one embodiment, logic transistors are formed in the periphery of the memory array before the diodes are formed in the memory array. In another embodiment, the diodes are formed in the memory array before the logic transistors are formed in the periphery of the memory array. The following description focuses solely on the memory array portion of the integrated circuit.

In one embodiment, a P substrate 202 is implanted with an N implant to form N+ region layer 204 a. In one embodiment, N− region layer 206 a is formed over N+ region layer 204 a using epitaxy, and P+ region layer 208 a is formed over N− region layer 206 a using epitaxy. In another embodiment, N− region layer 206 a and P+ region layer 208 a are formed using ion implantation into P substrate 202. In another embodiment, a combination of epitaxy and ion implantation is used to provide N− region layer 206 a and P+ region layer 208 a.

FIG. 9 illustrates a cross-sectional view of one embodiment of wafer 240 after forming a silicide layer 210 a. Silicide, such as CoSi, TiSi, NiSi, NiPtSi, WSi, TaSi, or other suitable silicide is formed over P+ region layer 208 a to provide silicide layer 210 a.

FIG. 10A illustrates a cross-sectional view of one embodiment of wafer 240 after depositing an electrode material layer. An electrode material, such as TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TIAlN, Cu, WN, C, or other suitable electrode material is deposited over silicide layer 210 a to provide electrode material layer 213 a. Electrode material layer 213 a is deposited using chemical vapor deposition (CVD), high density plasma-chemical vapor deposition (HDP-CVD), atomic layer deposition (ALD), metal organic chemical vapor deposition (MOCVD), physical vapor deposition (PVD), jet vapor deposition (JVD), or other suitable deposition technique. Wafer 240 as illustrated in FIG. 10A is used to fabricate memory cell 200 a previously described and illustrated with reference to FIG. 3 or memory cell 200 b previously described and illustrated with reference to FIG. 4.

FIG. 10B illustrates a cross-sectional view of one embodiment of wafer 240 after depositing a first electrode material layer 230 a, an etch stop material layer 232 a, and a second electrode material layer 216 a. In one embodiment, wafer 240 illustrated in FIG. 10B is used in subsequent processing steps in place of wafer 240 illustrated in FIG. 10A to fabricate memory cell 200 c previously described and illustrated with reference to FIG. 5.

An electrode material, such as TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, Cu, WN, C, or other suitable electrode material is deposited over silicide layer 210 a to provide first electrode material layer 230 a. First electrode material layer 230 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

An etch stop material is deposited over first electrode material layer 230 a to provide etch stop material layer 232 a. Etch stop material layer 232 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

The same electrode material that was deposited to provide first electrode material layer 230 a is deposited over etch stop material layer 232 a to provide second electrode material layer 216 a. Second electrode material layer 216 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

FIG. 10C illustrates a cross-sectional view of one embodiment of wafer 240 after depositing a first electrode material layer 234 a, an etch stop material layer 232 a, and a second electrode material layer 216 a. In one embodiment, wafer 240 illustrated in FIG. 10C is used in subsequent processing steps in place of wafer 240 illustrated in FIG. 10A to fabricate memory cell 200 e previously described and illustrated with reference to FIG. 7.

An electrode material, such as TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, Cu, WN, C, or other suitable electrode material is deposited over silicide layer 210 a to provide first electrode material layer 234 a. First electrode material layer 234 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

An etch stop material is deposited over first electrode material layer 234 a to provide etch stop material layer 232 a. Etch stop material layer 232 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

An electrode material different than the electrode material deposited to provide first electrode material layer 234 a, such as TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TIAlN, Cu, WN, C, or other suitable electrode material is deposited over etch stop material layer 232 a to provide second electrode material layer 216 a. Second electrode material layer 216 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

FIG. 10D illustrates a cross-sectional view of one embodiment of wafer 240 after depositing a first electrode material layer 234 a and a second electrode material layer 216 a. In one embodiment, wafer 240 illustrated in FIG. 10D is used in subsequent processing steps in place of wafer 240 illustrated in FIG. 10A to fabricate memory cell 200 d previously described and illustrated with reference to FIG. 6.

An electrode material, such as TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, Cu, WN, C, or suitable electrode material is deposited over silicide layer 210 a to provide first electrode material layer 234 a. First electrode material layer 234 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

An electrode material different than the electrode material deposited to provide first electrode material layer 234 a, such as TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, Cu, WN, C, or other suitable electrode material is deposited over first electrode material layer 234 a to provide second electrode material layer 216 a. Second electrode material layer 216 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

While the following FIGS. 11-26 illustrate the fabrication process of memory cell 200 a using wafer 240 illustrated in FIG. 10A, wafers 240 illustrated in FIGS. 10B-10D can be used in place of wafer 240 illustrated in FIG. 10A to fabricate memory cells 200 c-200 e using a similar fabrication process.

FIG. 11 illustrates a cross-sectional view of one embodiment of wafer 240 after forming a mask 242. A mask material or materials, such as photo resist, a hard mask material and photo resist, or other suitable mask material or materials are deposited over electrode material layer 213 a to provide a mask material layer. The mask material layer is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, spin on, or other suitable deposition technique. Using line lithography, the mask material layer is patterned and etched to provide lines of mask material forming mask 242.

In one embodiment, where the mask material layer includes photo resist, the photo resist is trimmed after the line lithography process to reduce the cross-sectional width of the lines of mask material to a sublithographic width. In one embodiment, where a hard mask material and photo resist is used, the photo resist is stripped after forming the lines of mask material. In another embodiment, where the mask material layer includes a hard mask, the hard mask material is trimmed using a wet etch or other suitable etch after the line lithography process to reduce the cross-sectional width of the lines of mask material to a sublithographic width. In another embodiment, where the mask layer includes a hard mask material and photo resist, a photo resist trim and etching of the hard mask material is performed after the line lithography process to reduce the cross-sectional width of the lines of mask material to a sublithographic width.

FIG. 12 illustrates a cross-sectional view of one embodiment of wafer 240 after etching electrode material layer 213 a. The exposed portions of electrode material layer 213 a are partially etched to provide electrode material layer 213 b. Electrode material layer 213 b includes a first portion 215 a and a second portion 217 a. Second portion 217 a provides lines of electrode material. First portion 215 a covers silicide layer 210 a.

In one embodiment, electrode material layer 213 a is etched to expose portions of silicide layer 210 a for fabricating memory cell 200 b previously described and illustrated with reference to FIG. 4. In another embodiment, where wafer 240 illustrated in FIG. 10B or FIG. 10C is used in place of wafer 240 illustrated in FIG. 10A, the etch stops on etch stop material layer 232 a. In another embodiment, where wafer 240 illustrated in FIG. 10D is used in place of wafer 240 illustrated in FIG. 10A, the etch stops on electrode material layer 234 a.

FIG. 13 illustrates a cross-sectional view of one embodiment of wafer 240 after depositing a spacer material layer 224 a. A spacer material, such as SiN, SiO₂, SiO_(x)N, or other suitable spacer material is conformally deposited over exposed portions of mask 242 and electrode material layer 213 b to provide spacer material layer 224 a. Spacer material layer 224 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

FIG. 14 illustrates a cross-sectional view of one embodiment of wafer 240 after etching spacer material layer 224 a. Spacer material layer 224 a is spacer etched to expose the top of mask layer 242 and portions of electrode material layer 213 b to provide spacers 224 b. Spacers 224 b contact the sidewalls of the lines of electrode material 217 a.

FIG. 15 illustrates a cross-sectional view of one embodiment of wafer 240 after etching trenches 244. Electrode material layer 213 b, silicide layer 210 a, P+ region layer 208 a, N− region layer 206 b, and an optional portion 205 of N+ region 204 a are etched self-aligned to spacers 224 b to provide trenches 244 and lines of electrode material 213 c, silicide lines 210 b, P+ region lines 208 b, N− region lines 206 b, and N+ region 204 b.

FIG. 16 illustrates a cross-sectional view of one embodiment of wafer 240 after depositing dielectric material 222 a into trenches 244. A dielectric material, such as SiO₂, SiO_(x), SiN, FSG, BPSG, BSG, or other suitable dielectric material is deposited over exposed portions of mask 242, spacers 224 b, lines of electrode material 213 c, silicide lines 210 b, P+ region lines 208 b, N− region lines 206 b, and N+ region 204 b to provide a dielectric material layer. The dielectric material layer, mask 242, and spacers 224 b are then planarized to remove mask 242, to expose lines of electrode material 213 c, and to provide spacers 224 c and dielectric material 222 a. The dielectric material layer is planarized using chemical mechanical planarization (CMP) or another suitable planarization technique. In one embodiment, mask 242 is removed before depositing and planarizing the dielectric material layer.

FIG. 17 illustrates a cross-sectional view of one embodiment of wafer 240 perpendicular to the cross-sectional view illustrated in FIG. 16. The cross-sectional view of FIG. 17 is taken along a line of electrode material 213 c. The cross-sectional view also includes a silicide line 210 b, a P+ region line 208 b, an N− region line 206 b, and N+ region 204 b. The following FIGS. 18-23 illustrate the same cross-sectional view as illustrated in FIG. 17.

FIG. 18 illustrates a cross-sectional view of one embodiment of wafer 240 after forming a mask 246. A mask material or materials, such as photo resist, a hard mask material and photo resist, or other suitable mask material or materials are deposited over lines of electrode material 213 c, spacers 224 c, and dielectric material 222 a to provide a mask material layer. The mask material layer is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, spin on, or other suitable deposition technique. Using line lithography, the mask material layer is patterned and etched to provide lines of mask material forming mask 246. The lines of mask material are perpendicular to the lines of electrode material 213 c.

In one embodiment, the mask material layer includes a lithographically defined photo resist layer. In another embodiment, where the mask material layer includes photo resist, the photo resist is trimmed after the line lithography process to reduce the cross-sectional width of the lines of mask material to a sublithographic width. In one embodiment, where a hard mask material and photo resist is used, the photo resist is stripped after forming the lines of mask material. In another embodiment, where the mask material layer includes a hard mask, the hard mask material is trimmed using a wet etch or other suitable etch after the line lithography process to reduce the cross-sectional width of the lines of mask material to a sublithographic width. In another embodiment, where the mask layer includes a hard mask material and photo resist, a photo resist trim and etching of the hard mask material is performed after the line lithography process to reduce the cross-sectional width of the lines of mask material to a sublithographic width.

FIG. 19 illustrates a cross-sectional view of one embodiment of wafer 240 after etching the lines of electrode material 213 c. The exposed portions of the lines of electrode material 213 c are etched to provide electrode material 213 d. Electrode material 213 d includes a first portion 215 c and second portions 216.

In one embodiment, the lines of electrode material 213 c are etched to expose portions of silicide layer 210 b for fabricating memory cell 200 b previously described and illustrated with reference to FIG. 4. In another embodiment, where wafer 240 illustrated in FIG. 10B or FIG. 10C is used in place of wafer 240 illustrated in FIG. 10A, the etch stops on etch stop material layer 232 a. In another embodiment, where wafer 240 illustrated in FIG. 10D is used in place of wafer 240 illustrated in FIG. 10A, the etch stops on electrode material layer 234 a.

FIG. 20 illustrates a cross-sectional view of one embodiment of wafer 240 after depositing a spacer material layer 248 a. A spacer material, such as SiN, SiO₂, SiO_(x)N, or other suitable spacer material is conformally deposited over exposed portions of mask 246 and electrode material 213 d to provide spacer material layer 248 a. Spacer material layer 248 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

FIG. 21 illustrates a cross-sectional view of one embodiment of wafer 240 after etching spacer material layer 248 a. Spacer material layer 248 a is spacer etched to expose the top of mask 246 and portions of electrode material 213 d to provide spacers 248 b. Spacers 248 b contact sidewalls of second portions 216 of electrode material 213 d. In one embodiment, the steps for forming spacers 248 b as illustrated and described with reference to FIGS. 20 and 21 are skipped and the fabrication process continues without spacers 248 b.

FIG. 22 illustrates a cross-sectional view of one embodiment of wafer 240 after etching trenches 250. Electrode material 213 d, silicide lines 210 b, P+ region lines 208 b, N− region lines 206 b, and N+ region 204 b are etched self-aligned to spacers 248 b to provide trenches 250 and bottom electrodes 212 a, silicide contacts 210, P+ regions 208, N− regions 206, and N+ word lines 204. In one embodiment, trenches 250 extend into P substrate 202 to ensure word line separation.

FIG. 23 illustrates a cross-sectional view of one embodiment of wafer 240 after depositing dielectric material 222 into trenches 250. A dielectric material, such as SiO₂, SiO_(x), SiN, FSG, BPSG, BSG, or other suitable dielectric material is deposited over exposed portions of mask 246, spacers 248 b, bottom electrodes 212 a, silicide contacts 210, P+ regions 208, N− regions 206, N+ word lines 204, and P substrate 202 to provide a dielectric material layer. The dielectric material layer, mask 246, and spacers 248 b are then planarized to remove mask 246, to expose bottom electrodes 212 a, and to provide spacers 248 and dielectric material 222. The dielectric material layer is planarized using CMP or another suitable planarization technique. In one embodiment, mask 246 is removed before depositing and planarizing the dielectric material layer.

FIG. 24 illustrates a cross-sectional view of one embodiment of wafer 240 after depositing a phase change material layer 218 a and an electrode material layer 220 a. The cross-sectional view illustrated in FIG. 24 is perpendicular to the cross-sectional view illustrated in FIG. 23. A phase change material, such as a chalcogenide compound material or other suitable phase change material is deposited over exposed portions of dielectric material 222, spacers 224, and bottom electrodes 212 a to provide phase change material layer 218 a. Phase change material layer 218 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

An electrode material, such as TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, TaAlN, Cu, WN, C, or suitable electrode material is deposited over phase change material layer 218 a to provide electrode material layer 220 a. Electrode material layer 220 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

FIG. 25 illustrates a cross-sectional view of one embodiment of wafer 240 after etching electrode material layer 220 a and phase change material layer 218 a. Electrode material layer 220 a and phase change material layer 218 a are etched to expose portions of dielectric material 222 and to provide phase change elements 218 and top electrodes 220. In one embodiment, phase change material layer 218 a and electrode material layer 220 a are etched in lines to form phase change elements 218 and top electrodes 220. In one embodiment, each line extends across the entire array of memory cells. In another embodiment, a number of shorter lines within each row of memory cells extend across the array of memory cells. In another embodiment, phase change material layer 218 a and electrode material layer 220 a are etched to form pillars above each bottom electrode 212 a to provide phase change elements 218 and top electrodes 220.

In another embodiment, phase change elements 218 are fabricated by first depositing a dielectric material, such as SiO₂, SiO_(x), SiN, FSG, BPSG, BSG, or other suitable dielectric material over bottom electrodes 212 a, spacers 224, and dielectric material 222 to provide a dielectric material layer. The dielectric material layer is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. The dielectric material layer is then etched to provide openings exposing bottom electrodes 212 a. A phase change material, such as a chalcogenide compound material or other suitable phase change material is deposited over the etched dielectric material layer and bottom electrodes 212 a to provide a phase change material layer. The phase change material layer is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. The phase change material layer is then planarized using CMP or another suitable planarization technique to expose the etched dielectric material layer and to provide phase change elements 218.

FIG. 26 illustrates a cross-sectional view of one embodiment of wafer 240 after depositing an encapsulation material layer 228 a and a dielectric material layer 226 a. Encapsulation material is deposited over exposed portions of top electrodes 220, phase change elements 218, and dielectric material 222 to provide encapsulation material layer 228 a. Encapsulation material layer 228 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. In one embodiment, more than one encapsulation material layer is deposited over top electrodes 220 and phase change elements 218.

A dielectric material, such as SiO₂, SiO_(x), SiN, FSG, BPSG, BSG, or other suitable dielectric material is deposited over encapsulation material 228 a to provide dielectric material layer 226 a. Dielectric material layer 226 a is deposited using CVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

Dielectric material layer 226 a and encapsulation material layer 228 a are etched to provide openings exposing top electrodes 220. A contact material is deposited into the openings. Upper metallization layers are then fabricated, including bit lines 112 coupled to top electrodes 220 through the contacts. In one embodiment, bit lines 112 are formed perpendicular to word lines 204.

Embodiments provide a resistive memory including resistivity changing memory elements accessed by vertical diodes. The memory cells are formed using a crossed line lithography fabrication process. The fabrication process includes forming the vertical diodes using a self-aligned process. In this way, a 4F² memory cell can be fabricated.

Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof. 

1. An integrated circuit comprising: a vertical diode defined by crossed line lithography.
 2. The integrated circuit of claim 1, further comprising: a silicide contact contacting the vertical diode; a first electrode coupled to the silicide contact; a spacer having a first sidewall contacting a first sidewall of the first electrode; a resistivity changing material coupled to the first electrode; and a second electrode coupled to the resistivity changing material, wherein a second sidewall of the spacer is aligned with a sidewall of the vertical diode and a second sidewall of the first electrode.
 3. The integrated circuit of claim 2, wherein the first electrode comprises an etch stop material layer contacting the spacer.
 4. The integrated circuit of claim 2, wherein the first electrode comprises a first electrode material contacting the silicide contact and a second electrode material contacting the resistivity changing material.
 5. The integrated circuit of claim 2, further comprising: an N+ word line coupled to the diode.
 6. The integrated circuit of claim 2, wherein the resistivity changing material comprises phase change material.
 7. The integrated circuit of claim 2, further comprising: at least one encapsulation material layer encapsulating the resistivity changing material and the second electrode.
 8. A system comprising: a host; and a memory device communicatively coupled to the host, the memory device comprising: a vertical diode including a first polarity region and a second polarity region; a silicide contact contacting the second polarity region; a first electrode coupled to the silicide contact; a spacer having a first sidewall contacting a first sidewall of the first electrode; a phase change element coupled to the first electrode; and a second electrode coupled to the phase change element, wherein a second sidewall of the spacer is aligned with a second sidewall of the first electrode and a sidewall of the vertical diode.
 9. The system of claim 8, wherein the memory device further comprises: a word line contacting the first polarity region; and a bit line coupled to the second electrode.
 10. The system of claim 8, wherein the memory device further comprises: a write circuit configured to program the phase change element.
 11. The system of claim 8, wherein the memory device further comprises: a sense circuit configured to read a state of the phase change element.
 12. The system of claim 8, wherein the memory device further comprises: a controller configured to control read and write operations of the phase change element.
 13. A memory comprising: a first polarity region; a second polarity region contacting the first polarity region; a silicide contact contacting the second polarity region; a first electrode coupled to the silicide contact; a spacer having a first sidewall contacting a first sidewall of the first electrode; a resistive memory element coupled to the first electrode; and a second electrode coupled to the resistive memory element, wherein a second sidewall of the spacer is aligned with a second sidewall of the first electrode, a sidewall of the silicide contact, a sidewall of the second polarity region, and a sidewall of the first polarity region.
 14. The memory of claim 13, wherein the first electrode comprises an etch stop material layer contacting the spacer.
 15. The memory of claim 13, wherein the first electrode comprises a first electrode material contacting the silicide contact and a second electrode material contacting the resistive memory element.
 16. The memory of claim 13, wherein the first polarity region comprises an N− region, and wherein the second polarity region comprises a P+ region.
 17. The memory of claim 16, further comprising: an N+ word line contacting the N− region, the N+ word line having a sidewall self-aligned with the second sidewall of the spacer.
 18. The memory of claim 13, further comprising: at least one encapsulation material layer encapsulating the resistive memory element and the second electrode.
 19. The memory of claim 13, wherein the resistive memory element comprises a phase change element.
 20. A method for fabricating a memory cell, the method comprising: providing a wafer including a first polarity region layer, a second polarity region layer over the first polarity region layer, a third polarity region layer over the second polarity region layer, a silicide layer over the third polarity region layer, and electrode material over the silicide layer; etching the electrode material to form a line of electrode material; forming spacers on sidewalls of the line of electrode material; etching the silicide layer, third polarity region layer, and second polarity region layer self-aligned to sidewalls of the spacers to form a silicide line, a third polarity region line, and a second polarity region line; etching the line of electrode material, silicide line, third polarity region line, and second polarity region line to form a first electrode, a silicide contact, and a diode; fabricating a resistive memory element contacting the first electrode; and fabricating a second electrode contacting the resistive memory element.
 21. The method of claim 20, wherein providing the electrode material comprises providing a first electrode material layer over the silicide layer, an etch stop material layer over the first electrode material layer, and a second electrode material layer over the etch stop material layer, and wherein etching the electrode material comprises etching the second electrode material layer.
 22. The method of claim 20, wherein providing the electrode material comprises providing a first electrode material layer over the silicide layer and a second electrode material layer over the first electrode material layer, and wherein etching the electrode material comprises etching the second electrode material layer.
 23. The method of claim 20, wherein etching the electrode material comprises etching the electrode material to expose a portion of the silicide layer.
 24. The method of claim 20, further comprising: etching the first polarity region layer to provide a first polarity word line contacting the diode.
 25. The method of claim 20, wherein fabricating the resistive memory element comprises fabricating a phase change element.
 26. The method of claim 20, wherein providing the wafer comprises providing the wafer including the first polarity region layer comprising an N+ region layer, the second polarity region layer comprising an N− region layer, and the third polarity region layer comprising a P+ region layer.
 27. A method for fabricating a memory cell, the method comprising: fabricating a first polarity region; fabricating a second polarity region on the first polarity region; fabricating a third polarity region on the second polarity region; forming a silicide on the third polarity region; depositing a first electrode material layer over the silicide; etching the first electrode material layer to provide a line of first electrode material; forming first spacers on sidewalls of the line of first electrode material; etching the silicide, the third polarity region, and the second polarity region self-aligned to sidewalls of the first spacers to form first trenches; depositing dielectric material into the first trenches; etching the line of first electrode material to provide a first electrode; forming second spacers on sidewalls of the first electrode, the second spacers perpendicular to the first spacers; etching the silicide, the third polarity region, and the second polarity region self-aligned to sidewalls of the second spacers to form second trenches, a silicide contact, and a diode; depositing dielectric material into the second trenches; depositing a phase change material layer over the first electrode; depositing a second electrode material layer over the phase change material layer; and etching the second electrode material layer and the phase change material layer to provide a phase change element contacting the first electrode and a second electrode contacting the phase change element.
 28. The method of claim 27, further comprising: etching the first polarity region self-aligned to sidewalls of the second spacers to provide a first polarity word line contacting the diode.
 29. The method of claim 27, wherein etching the first electrode material layer comprises etching the first electrode material layer to expose a portion of the silicide.
 30. The method of claim 27, further comprising: depositing at least one encapsulation material layer over the second electrode and the phase change element.
 31. The method of claim 27, wherein fabricating the first polarity region comprises fabricating an N+ region; wherein fabricating the second polarity region comprises fabricating an N− region; and wherein fabricating the third polarity region comprises fabricating a P+ region.
 32. A method for fabricating an integrated circuit, the method comprising: providing a wafer including a first polarity region layer and a second polarity region layer over the first polarity region layer; and etching the first polarity region layer and the second polarity region layer using a crossed line lithography process to form vertical diodes from the first polarity region layer and the second polarity region layer. 